docs: def get_mean_and_stddevs(self, sites, rup, dists, imt, stddev_types):
          """
          See :meth:`superclass method
          <.base.GroundShakingIntensityModel.get_mean_and_stddevs>`
          for spec of input and result values.
          """
          # extracting dictionary of coefficients specific to required
          # intensity measure type.
          C = self.COEFFS[imt]
          C_PGA = self.COEFFS[PGA()]
          imt_per = 0 if imt.name == 'PGV' else imt.period
          pga_rock = self._get_pga_on_rock(C_PGA, rup, dists)
          mean = (self._get_magnitude_scaling_term(C, rup) +
                  self._get_path_scaling(C, dists, rup.mag) +
                  self._get_site_scaling(C, pga_rock, sites, imt_per, dists.rjb))
          stddevs = self._get_stddevs(C, rup, dists, sites, stddev_types)
          return mean, stddevs